The chief executive of BP, Bob Dudley, warns of the uncertainties surrounding
an independent Scotland's currency and states that Great Britain "ought
to stay together"

The head of oil multinational BP has delivered a major blow to Alex Salmond’s economic case for independence after becoming the most high-profile business leader yet to publicly attack Scottish independence.

Bob Dudley said that “Great Britain is great and it ought to stay together” after being asked about the impact of Scottish separation on his company.

He told the BBC there were “big uncertainties” surrounding a separate Scotland’s currency and membership of the EU and “all businesses” are worried.

Although he said the company was pressing ahead with its investment plans in Scotland for the time being – BP was the first firm to strike oil in the North Sea – Mr Dudley said independence represented a "question mark" for the firm.

Mr Dudley’s intervention represents a serious blow to Mr Salmond and his fellow separatists as their economic case for separation relies heavily on North Sea tax revenues.

It also provides further evidence that major business leaders are starting to go public with their concerns about separation, having faced major criticism for staying silent until now amid claims of SNP intimidation.

In a double blow for Mr Salmond, the leaders of another industry vital to his separatist blueprint, financial services, today reiterated their warning that independence would cost them millions of pounds.

BP remains the largest UK investor in the North Sea and one of the world’s biggest companies. The firm plans to invest £10 billion in the North Sea between 2011 and 2016, its highest ever investment in the region.

Mr Dudley said: “We have a lot of people in Scotland, we’ve got a lot of investments in Scotland. I don’t know … there’s much debate about what would happen with the currency and of course whether there would be connections with Europe or not.

“These are quite big uncertainties for us. At the moment we’re continuing to invest at the (same) pace because these projects are under way.

“But it’s a question mark. I think all businesses have a concern. My personal view is Great Britain is great and it ought to stay together."

The American told the BBC Scottish separation would mean BP having two head offices, which would create additional costs.

Alistair Darling, the former Labour Chancellor and leader of the pro-UK Better Together campaign, said: "This is perhaps the biggest intervention by a major business so far in the referendum debate.

"I hope that more companies and business leaders speak out over the coming weeks and months. This debate is far too important to be left to politicians alone. Bob Dudley is quite right to express concern about the issue of currency. It is far from certain what currency we would use if we vote to leave the UK.”

Tom Greatrex MP, Labour's Shadow Energy Minister, called for other business leaders to follow suit, adding: "Bob Dudley has made clear that the unanswered questions arising from the SNP’s desire to see Scotland leave the UK are a cause of significant concern to his business – and will be a concern to thousands of other businesses, large and small.

"The SNP’s efforts to separate Scotland from the rest of the UK are a palpable threat to the jobs and investment here in Scotland."

But a Scottish government spokesman said BP already operates in more than 80 countries. He said: "We welcome all contributions to the debate on Scotland's future, and would be happy to meet with Mr Dudley to discuss the future of the industry in an independent Scotland. He has made clear these are his personal views and that the company is continuing to invest in Scotland.

"Record amounts of money are being invested in the offshore sector, by BP and others, with £100 billion of investment planned by companies. And more than half of oil and gas reserves by value are still to be extracted."

A spokesman for the pro-separation Yes Scotland campaign said: “A shared currency is in the overwhelming economic interests of both Scotland and the rest of the UK.”

However, the Nationalists have refused to name their Plan B despite George Osborne, the Chancellor, stating such a eurozone-style deal would be unlikely after independence.

Mr Salmond has repeatedly claimed there is up to £1.5 trillion of oil and gas left in the North Sea, although the Treasury has said around a £1 trillion would have to be spent to extract it from reserves that are becoming hard to reach.

The Scottish government’s recent White Paper on independence promised to set up an oil fund whereby tax revenues would be squirrelled away for future generations instead of spent on day-to-day public services.

But economists and the SNP’s political opponents have warned this would require extra spending cuts or tax increases as all North Sea revenues are currently swallowed up by public expenditure.

A recent report by the Institute for Fiscal Studies said that even without an oil fund, a separate Scotland would have to make an extra £6 billion of spending cuts and tax rises thanks to declining North Sea revenues.

In another blow, Scottish Financial Enterprise, which represents the country’s multi-billion pound pensions, banking and life insurance industry, has repeated its warning separation would mean hiring hundreds of staff for a new regulator.

Owen Kelly, the trade body’s chief executive, told the Financial Times: “The cost would run into millions and have to be paid for by the industry in Scotland.”

He said fund managers would need to tailor their products and services for Scottish clients to a new tax, consumer protection and regulatory regime, creating additional complexity and costs.

Mr Kelly told the Telegraph last year any extra costs for products such as mortgages would have to be passed onto customers.

We reported earlier this week how Brian Quinn, a former Deputy Governor of the Bank of England, said financial services firms are facing a dilemma between keeping secret their concerns about independence and risking losing a large proportion of their customers.

Asked about Mr Dudley's comments, Prime Minister David Cameron's official spokesman said: "I think it is important when one of the UK's leading businesses and investors and an important employer raises this issue.

"He is making a very important point."

Several Government ministers have already made clear that it is "highly unlikely" that an independent Scotland would be able to join a currency union with the remaining UK, said the spokesman.

A Scottish Government spokesman said: "We welcome all contributions to the debate on Scotland's future, and would be happy to meet with Mr Dudley to discuss the future of the industry in an independent Scotland.

"He has made clear these are his personal views and that the company is continuing to invest in Scotland.

"BP is a company which already operates in more than 80 independent countries around the globe, and an independent Scotland with full control of its economy and huge resources will offer an attractive and stable environment for businesses in the offshore and other sectors.

"An independent Scotland will keep the pound as part of a sterling area, which is in the overwhelming economic interests of the rest of the UK."